Over the years, the cost of rising fuel has become more and more of a concern. However, with the increase of fuel costs to over $100 per barrel of oil, the concern over fuel costs has never been greater. The significant rise in fuel costs coupled with the federal government's strategy of becoming less dependent on foreign oil has lead to the federal government (and some state governments) beginning the process of tightening semi-truck regulations with regard to this particular industry's fuel efficiency. A significant way of improving fuel economy on any vehicle is through improving the vehicle's aerodynamic efficiencies (mainly through aerodynamic drag reduction).
The trucking industry plays a significant role in our country's day to day functioning. A key for the trucking industry is the ability to transport as much product as possible per payload (i.e. cubing out each load). Therefore, removing loading capacity will significantly hurt the performance and functionality of the trucking industry. Because of this, the best aerodynamic improvements will be the ones that allow for the existing payload capacity while these aerodynamic devices are implemented. Aside from payload capacity, an aerodynamic device must be practical and not interfere with day to day operations (i.e. allowing for rear trailer doors to open 225° for loading and unloading). On top of all this, any aerodynamic device must not be a maintenance issue or cost prohibitive.
Several groups have tried to address the needs in this area for semi-trucks over the last many decades with mixed success. Multiple patents have been issued that meet one, or at most two, of the above criteria, but none that meet all of these. This is mostly due to the developmental techniques available throughout these different patent filing times. For the first time in U.S. history, a semi-truck can now be modeled in a very accurate way under severely controlled conditions.
The use of a rolling road wind tunnel and a ⅛ scale semi-truck model has revolutionized the ability for fuel economy improvements in the trucking industry. Until 2008, the best developmental practice in the trucking industry was through actual on-road testing. Real world on-road testing could not allow the developer the ability to control testing variables and led to a large lack of accuracy. Some of the uncontrollable variables include, but are not limited to, driver, traffic, ambient conditions, fuel measurement accuracies, cross wind, tire degradation, engine efficiencies, payload capacities, route differences, altitude differences and many more. All of these variables are controlled with rolling road wind tunnel testing.
NASA built a ⅛ scale semi-truck model and tested it in various wind tunnels throughout the U.S. including a Reynolds sweep tunnel. All of these wind tunnels were fixed floor (i.e. non-rolling road). NASA's conclusions were that a ⅛ scale model of a semi-truck could accurately represent the real world airflows if tested with a Reynolds number above 1.1 M. An identical NASA model (NASA provided the detailed manufacturing drawings) was built and the next progressive step of testing this ⅛ scale semi-truck model with a rolling road wind tunnel above Re=1.1 M was taken. The results of this ground breaking work conclusively showed that without a rolling road (and rotating wheel) testing environment over 85% of the items tested gave an opposite performance trend than was witnessed in a fixed floor wind tunnel environment. This meant that 85% of the items developed in a fixed floor wind tunnel actually increased the drag of the vehicle instead of reducing the drag even though the results from the fixed wind floor tunnel tests showed an over-all drag reduction. This one rolling road test changed the outlook for the future of semi-truck development.
Because testing in a rolling road wind tunnel allows all of the real-world testing variables to be controlled, rolling road wind tunnel testing allows for an accuracy of 0.25% changes in fuel economy to be measured (as opposed to 1-1.5% with on road under the strictest of conditions). Therefore, utilizing a rolling road wind tunnel has become the most cost effective way to develop the semi-truck aerodynamics.
Prior art shows details of turning vanes at the trailing edges of semi-trailers. Some do not allow for the doors to be opened to the standard 225°. Others actually do not give any aerodynamic benefit. The placement of aerodynamic devices is critical to their success. Some of the prior art has attached turning vanes that do not allow a gap between the vane and the trailer. These concepts are essentially extending the trailing edge of the trailer and simply increasing the corner radii.
U.S. Pat. No. 3,960,402 describes vehicle flow direction vanes for reducing the rear vacuum induced drag on moving vehicles. This patent does not offer the 20% improvement in mileage as claimed (which would actually require a 40% over all drag reduction). At best, this vane provides 0.5% improvement in fuel economy as measured in a rolling road wind tunnel. This device also does not allow the trailer doors to open 225° for loading and unloading. This device also includes angles of 30° of curvature for its peak performance. This device claims to create a “high velocity cone” at the rear of the trailer but does not improve the tip shedding.
U.S. Pat. No. 3,999,797, describes an airvane for use with bluff vehicles which is used to reduce separation to reduce air drag and buffeting of the vehicle. This prior art claims an airvane that mounts on the front and rear of the top and sides of a trailer. These mountings are permanent and do not allow the trailer doors to open 225° for their normal usage. It is also claimed that these devices must work in concert with each other. This device does not give the claimed drag reduction.
U.S. Pat. No. 7,240,958 B2 refers to an apparatus with flexible attachments for reducing the drag on a vehicle having a generally planar surface. The connections, or flexible attachments utilize cables mounted to vanes. This patent basically claims the use of only rear mounted vanes on the semi-trailer for drag reduction. This device does not give the claimed drag reduction.